Method of making yttrium-aluminumiron garnets



Oct. 31, 1961 B. A. CALHOUN ETAL 3,006,856

METHOD OF MAKING YTTRIUM-ALUMINUM-IRON GARNETS Filed Dec. 31. 1959 2 Sheets-Sheet 2 1s 4 0 (SLOW coon 12 AIR (SLQW COOL) '5 9 7 Q 1 LL! I AIR c: In 8 0 v TEMPERATURE (C) United States ?Etii1t iliiiice 3,006,856 Patented Oct. 31, 1961 3,096,856 METHOD OF MAKING YTTRiUld-ALUMIhFJh l- IRON GAHQETS Bertram A. Calhoun and Wilbert L. Shovel, 3:2, Poughkeepsie, N.Y., assignors to International Business Machines Corporation, New York, N.Y., a corporation at New York Filed Dec. 31, 1959, Ser. No. 363,320 8 Claims. (Cl. 252-625) This invention relates to low magnetic moment garnets and more particularly to a method of preparing such garnets for application as high speed switching elements in computer circuitry.

Present day schemes for high-speed switching of magnetic elements are limited by overheating of the individual elements, For example, the use of the bistable, square hysteresis loop ferrite materials, as memory storage elements in computers is severely limited by the excessive heating of the elements during the switching operation. These elements thereupon require elaborate cooling procedures and/or operation at low repetition rates in order to overcome the overheating efifect. The development of a suitable low moment magnetic material would permit operation at repetition frequencies limited only by the switching time of the material.

There are two distinct advantages to the use of a low moment material for switching operations, such as memory storage and pulse transfer.

First, as mentioned above, there is a decrease in the power dissipation during the switching operation. The power dissipated. in an element during switching is proportional to (AI )(NI) (f), where A I is the amount of flux reversed, N1 is the driving current, and f is the number of times per second that the element is switched.

Secondly, low moment materials induce a lower back voltage in the drive windings.

At present a serious objection. to the use of low moment materials at moderate or low speeds is the decreased output voltage which these materials provide At high speed operation, however, this limitation no longer is present since the output voltage increases proportionately with the switching speed.

It is therefore of considerable interest to provide low magnetic moment garnet materials, suitable for operation in computer circuitry which have low switching constants and are capable therefore of operating at high switching speeds with high output voltages.

A number of. ferromagnetic garnets with low magnetic moments and methods of preparing the same have been reported in'the literature. In general these materials have a low remanence, high coercive forces and relatively slow switching speeds. Low moment ferrites on the other hand, exhibit a high remanence and low coercive forces but have exceedingly slow switching speeds and thus give an intolerably low output voltage for computer use.

According to the present invention a method of 'preparing high speed, low magnetic moment garnets has been provided which method produces products which are particularly suitable for use as switching elements in computer circuitry. In particular these elements exhibit a low power dissipation during switching operation, a decreased back voltage induction in the drive lines, a high output voltage, fast switching speeds, a high remanence and low coercive forces.

An object of the present invention is to provide a method of preparing low magnetic moment garnets which are suitable for high speed switching operation in computer circuitry,

A further object is to provide memory garnets having low moments and which exhibit a high output voltage during the switching operation.

Still another object of the instant invention is to provide methods of preparing storage garnet elements having a low power dissipation, a low moment, a relatively high remanence, a high switching speed, a high output voltage and relatively low coercive forces.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a graphic representation in which is plotted the switching coeflicient, S versus sintering temperature for a low moment garnet material prepared according to the practice of the present invention.

FIGURE 2 is a plot of the rotational coercive force, H vs. sintering temperature for the same material prepared by a similar process.

According to the present invention low magnetic mo ment ferromagnetic garnets suitable for operation as switching elements in computer circuitry have been provided. Specifically the method of the present invention involves sintering the garnet constituents at elevated tem Examples Garnets of composition Y AlFe O were prepared: by mixing 1:6 gram of A1 0 and 6.3 grams of Fe O calcining the oxide powders at approximately 1000' in air for one hour, then mixing the powders with 6.7. grams or" 1 0 and further calcining the mixture at 1300 C. hr air for an additional one hour.

a pressed into cores of 30 mils inside diameter and 50 s outside. diameter and 12 mils thickness. bodies thus prepared were fired in an oxygen oxidizing atmosphere, such as air or 0 at 1440-1470 C. for a time sufficient to form the garnet structure, 8 hours- After sintering; the.

being an ample period of time. core bodies were quenched to room temperature on a metal plate in air durin about two minutes. The garnets thus prepared exhibited a flux density at saturation, B or" about 190 gausses and a retained flux density, B,, of about gausses. The switching threshold I-I, was. 1.2 oersteds and the output voltage 30 millivolts;

FEGURE 1 shows the efiect of the sintering temperature and the cooling rate on the switching constants of garnets of the composition Y AlFe4O Core: bodies which were sintered within. the temperature. range 1440 1470 C. in an oxygen oxidizing atmosphere and rapidly quenched are shown to possess switching constants, S

which correlate to operational switching timesof the order of 4 to 5 times faster than similar compositions prepared by sintering the core body at temperatures below this range. Sintering temperatures above this range are not useabie since the garnet begins to decompose about i470 C.

FIGURE 1 also shows the effect of slow cooling the same core body from the sintering temperature to room temperature in the sintering atmosphere over a period of about 1 hour as contrasted to rapid quenching. Slow cooling increases the switching constant by a factor of 2.

The high speed, S about 0.20, low moment, B about 200' garnets of the present invention provide useable output signals of 30 millivolts or more. Amplification of signals below 30 millivolts is not feasible with Garnets pro- The calcined powders The core present day equipment. In addition, the slow cooled products are totally unsuitable as switching elements in 1470 C. and in produces products having H values 'of about 4 oersteds and in air about 4.59 oersteds.

The method of the present invention consists essentially of sintering the garnet constituents in the range 1440- 1470 C. in an oxygen oxidizing atmosphere and fast quenching the sintered product to room temperature. A loW' moment garnet particularly suitable for computer use is obtained by sintering the garnet powders at 1460 C. in air and fast quenching to room temperature. A low coercive force garnet is obtained by sintering at 1450 C. in 0 and fast quenching.

Various substitutions for Y, Al or Fe may be made as is known in the art as long as the resultant low moment garnet possesses a B /B ratio of at least 0.5, the

lower limit for use of these materials as switching elements in two dimensional memory arrays or as in matrix switching devices.

j While every variation in composition in the garnet series has not been described the method of the present invention may be generally applied to garnet materials to improve their magnetic characteristics as described.

While we have shown a preferable presintering or cal-' cining treatment it is to be understood that other calcining schemes may be practiced as are known in the art.

What has been described herein is a method of preparing high speed, low coercive force, low moment garnets having a B /B ratio of about 0.7, which method involves sintering the garnet powders at elevated temperatures in the range 1440l470 C. in an oxygen oxidizing atmosphere and rapidly quenching the thus formed garnet to room temperature. Garnets thus prepared have low magnetic moments, in the order of about 200 gausses, switching constants in the order of 0.11 oerstedmicrosecond and an output voltage of greater than 30 millivolts. The high speed garnets thus prepared are particularly desirable in application in computer circuitry in that they do not overheat during the switching operation and do not induce a large back voltage in the drive lines.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. The method of preparing high speed, low moment yttrium-aluminum-iron garnets of the composition 3 4 12 which comprises providing calcined powders of Y 0 A1 0 and F6203 in proportions corresponding to said for mula, sintering said powders at elevated temperatures in the range 14401470 C. in an oxygen oxidizing atmosphere for about 8 hours and quenching the garnet formed to room temperature.

2. The method according to claim 1 wherein said atmosphere is air. 7

3. The method according to claim 1 wherein said oxidizing atmosphere is 0 4. The method of preparing high speed, low moment yttrium-aluminum-iron garnets of the :composition which comprises providing calcined powders of Y O A1 0 and Fe O in proportions corresponding to said formula, sintering said powders at 1460 .C. in an air atmosphere for 8 hours andquenching the garnet formed to room temperature during two minutes, said garnet having the following magnetic properties: B gausses, S =0.ll oersted-microsecond, B /B =0.7 and H =8.2 oersteds.

5. The method of preparing high speed, low moment yttrium-alurnium-iron garnets of the composition which comprises providing calcined powders of Y O A1 0 and Fe fi in proportions corresponding to said formula, sintering said powders at 1450" C. in an O atmosphere for 8 hours and quenching the garnet formed to room temperature during two minutes, said garnet having the following magnetic properties, B :190 gausses, S :0.l2, B /B =G.7 and H =3.S oersteds.

6. The method of preparing high speed, low moment yttrium-alumium-iron garnets of the composition which comprises providing 1.0 gram of A1 0 and 6.3 grams of Fe O calcining said powders at 1600 C. in air for one hour, mixing the calcined powders with 6.7 grams of 0 further calcining the mixture at 1360' C. in air for an additional hour, shaping said powders into core bodies of 30 mils inside diameter, 50 mils outside diameter and 12 mils thickness, sintering said bodies in a temperature range of 1440-1470" C. for 8 hours in an oxygen oxidizing atmosphere and quenching the garnet formed to room temperature during two minutes.

7. The method according to claim 6 wherein said atmosphere is air and said sintering temperature is 1460 C.

8. The method according to claim 6 wherein said atmosphere is 0 and said sintering temperature is 1450 C.

References Cited in the file of this patent Calhoun: IBM Tech. Disclosure Bull., vol. 1, No. 2, p. 26 (August 1958).

Pauthenet: Proceedings 4th Symposium Magnetism and Magnetic Materials, pp. 290S292S, April 1959.

Calhoun: Proceedings 4th Symposium Magnetism and Magnetic Materials, pp. 2938-2948, April 1959. 

6. THE METHOD OF PREPARING HIGH SPEED, LOW MOMENT YTTRIUM-ALUMINUM-IRON GARNETS OF THE COMPOSITION 